<!DOCTYPE html>

<html lang="en">
<head>
<meta charset="utf-8" />
<title>Downward Edges</title>
<style>
@import url(../style.css);

.node {
  stroke: #fff;
  stroke-width: 1.5px;
}

.link {
  fill: none;
  stroke: #000;
  stroke-width: 1.5px;
  opacity: 0.4;
  marker-end: url(#end-arrow);
}

</style>
</head>
<body>
    <a href="../index.html">cola.js home</a>
<h1>Directed Graph with downward-pointing edges</h1>
<script src="../extern/d3v4.js"></script>
    <script src="../cola.min.js"></script>
<script>
    var width = 960,
        height = 500;

    var color = d3.scaleOrdinal(d3.schemeCategory20);

    var d3cola = cola.d3adaptor(d3)
        .avoidOverlaps(true)
        .size([width, height]);

    var svg = d3.select("body").append("svg")
        .attr("width", width)
        .attr("height", height);

    d3.json("graphdata/chris.json", function (error, graph) {
        var nodeRadius = 5;

        graph.nodes.forEach(function (v) { v.height = v.width = 2 * nodeRadius; });

        d3cola
            .nodes(graph.nodes)
            .links(graph.links)
            .flowLayout("y", 30)
            .symmetricDiffLinkLengths(6)
            .start(10,20,20);

        // define arrow markers for graph links
        svg.append('svg:defs').append('svg:marker')
            .attr('id', 'end-arrow')
            .attr('viewBox', '0 -5 10 10')
            .attr('refX', 6)
            .attr('markerWidth', 3)
            .attr('markerHeight', 3)
            .attr('orient', 'auto')
          .append('svg:path')
            .attr('d', 'M0,-5L10,0L0,5')
            .attr('fill', '#000');

        var path = svg.selectAll(".link")
            .data(graph.links)
          .enter().append('svg:path')
            .attr('class', 'link');

        var node = svg.selectAll(".node")
            .data(graph.nodes)
          .enter().append("circle")
            .attr("class", "node")
            .attr("r", nodeRadius)
            .style("fill", function (d) { return color(d.group); })
            .call(d3cola.drag);

        node.append("title")
            .text(function (d) { return d.name; });

        d3cola.on("tick", function () {
            path.each(function (d) {
                if (isIE()) this.parentNode.insertBefore(this, this);
            });
            // draw directed edges with proper padding from node centers
            path.attr('d', function (d) {
                var deltaX = d.target.x - d.source.x,
                    deltaY = d.target.y - d.source.y,
                    dist = Math.sqrt(deltaX * deltaX + deltaY * deltaY),
                    normX = deltaX / dist,
                    normY = deltaY / dist,
                    sourcePadding = nodeRadius,
                    targetPadding = nodeRadius + 2,
                    sourceX = d.source.x + (sourcePadding * normX),
                    sourceY = d.source.y + (sourcePadding * normY),
                    targetX = d.target.x - (targetPadding * normX),
                    targetY = d.target.y - (targetPadding * normY);
                return 'M' + sourceX + ',' + sourceY + 'L' + targetX + ',' + targetY;
            });

            node.attr("cx", function (d) { return d.x; })
                .attr("cy", function (d) { return d.y; });
        });
        // turn on overlap avoidance after first convergence
        //cola.on("end", function () {
        //    if (!cola.avoidOverlaps()) {
        //        graph.nodes.forEach(function (v) {
        //            v.width = v.height = 10;
        //        });
        //        cola.avoidOverlaps(true);
        //        cola.start();
        //    }
        //});
    });

    function isIE() { return ((navigator.appName == 'Microsoft Internet Explorer') || ((navigator.appName == 'Netscape') && (new RegExp("Trident/.*rv:([0-9]{1,}[\.0-9]{0,})").exec(navigator.userAgent) != null))); }
</script>

<p>Pairs of nodes connected by an edge have a vertical separation constraint, requiring that the source be a minimum distance above the target.
   We also require that node bounding boxes cannot overlap.
     The unconstrained layout of the same graph looks like <a href="unconstrained.html">this</a>.
    </p>
    <p>Here's <a href="3dtree.html">a 3D version</a> of the same graph!</p>
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